Lipids Flashcards
What are the major lipid classes
fatty acids
triacylglycerol
phospholipids
steroid
glycolipid
Role of fatty acids
Fatty acids are the building blocks of the fat in our bodies and in the food we eat
Fatty acids have many important functions in the body, including energy storage
If glucose isn’t available for energy, the body uses fatty acids to fuel the cells instead
Role of triacylglycerols (TAG)
esters of FA’s and glycerol
water insoluble TAC coalesce into lipid droplets in adipose tissues
dietary fuel and insulation
most TAG degraded in small intestine by pancreatic lipase to monocylglycerol and FA
Role of Phospholipids
composed of glycerol bonded to two fatty acids and a phosphate group
amphipathic - hydrophilic head and hydrophobic tail
walls of cell membrane
Digestion of lipids
triacylglycerol main dietary lipid
small intestine - main site of digestion
lipid digestion by pancreatic enzymes (lipase) promoted by emulsification by bile salts and peristalsis
Absorption of lipids
products of lipid digestion form mixed micelles with bile salts
mixed micelles approach brush border membranes of enterocytes and release lipid products which enter by diffusion
short and medium chain FA do not require micelles for absorption
How are lipids transported in the body
free FA transported through blood in complex with serum albumin
albumin most abundant plasma protein with 2-7 binding site for FA
most FA esterified
carried in lipoproteins
TAG’s and cholesterol esters are insoluble in water and cannot be transported in blood or lymph as free molecules
Role of lipoproteins
to transport water-insoluble lipids from their point of origin to their respective destinations.
Synthesis of free fatty acids
occurs in liver, lactating mammary gland, adipose tissue
synthesised from acetyl CoA, derived from excess protein, fat, carbohydrate
occurs in cytosol, uses ATP and NADG
What are essential fatty acids
Humans cannot introduce double bonds beyond carbon 9
must be ingested
Catabolism of fatty acids by beta-oxidation
degrades 2 carbons at a time between alpha and beta carbons
produces acetyl CoA and also NADH and FADH2 which are sources of energy (ATP)
occurs in mitochondrial matrix
three stages-
- Activation of fatty acids in the cytosol
- Transport into the mitochondria by Carnitine shuttle
- Degradation to 2 carbon fragments (as Acetyl CoA) in the mitochondrial matrix - energy
Structure and function of cholesterol
function - component of cell membrane, precursor to other substances: steroid hormones, vitamin D, bile salts
structure - a hydrocarbon tail, a central sterol nucleus made of four hydrocarbon rings, and a hydroxyl group.
Structure and function of eicosanoids
Function - regulate: inflammatory response, pain & fever, blood pressure regulator, blood clotting induction/platelet homeostasis, many reproductive functions, mucus production in stomach
structure - derived from 20-carbon unsaturated FA, signalling molecule derived from Omega-3 or Omega-6 FA, short half-life
Structure and function of steroids
structure - arranged in four rings conventionally denoted by the letters A, B, C, and D—bonded to 28 hydrogen atoms
function - as important components of cell membranes which alter membrane fluidity; and as signalling molecules
Synthesis of ketone bodies
Ketone bodies are synthesised as an alternative source of energy when intracellular glucose concentration can not meet metabolic demands
Ketone bodies are synthesised from acetyl-coenzyme A (acetyl-CoA) which is a product of mitochondrial β-oxidation of fatty acids
formed in the liver (mitochondrial matrix)
